Suggestion: mention string interning

还没有人认领这个 Issue。

If we want to be completely clear in the [object copy lesson](https://javascript.info/object-copy), we can include a snippet that mentions string interning, where since strings are immutable, only one instance is stored in memory and any future references to that same string can be referred to the singleton in existence. So yes, primitives are "copied as a whole value" in behavior, but it's a little bit more complicated than that if we get into implementation detail.

Is this too much? Thoughts? JavaScript.info seems to be a pretty thorough resource, so I can definitely see it including this kind of detail.

从链接的对象复制课程开始，检查课程目前如何解释原始值和字符串行为。确定字符串驻留是否应纳入课程，然后仅在公开讨论达成决定后更新说明；完成的标准是课程准确反映约定的实现细节程度。

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